diff --git a/apps/files_external/lib/Service/UserStoragesService.php b/apps/files_external/lib/Service/UserStoragesService.php
index 6cf34000ab009..47a6e919853ab 100644
--- a/apps/files_external/lib/Service/UserStoragesService.php
+++ b/apps/files_external/lib/Service/UserStoragesService.php
@@ -127,6 +127,9 @@ public function addStorage(StorageConfig $newStorage) {
 	 * @throws NotFoundException if the given storage does not exist in the config
 	 */
 	public function updateStorage(StorageConfig $updatedStorage) {
+		// verify ownership through $this->isApplicable() and otherwise throws an exception
+		$this->getStorage($updatedStorage->getId());
+
 		$updatedStorage->setApplicableUsers([$this->getUser()->getUID()]);
 		return parent::updateStorage($updatedStorage);
 	}